Thermogravimetric analysis, PXRD, EDX and XPS study of chrysocolla (Cu,Al)2H2Si2O5(OH)4·nH2O-structural implications

Abstract

Selected chrysocolla mineral samples from different origins have been studied by using PXRD, SEM, EDX and XPS. The XRD patterns show that the chrysocolla mineral samples are non-diffracting and no other phases are present in the minerals, thus showing the chrysocolla samples are pure. SEM analyses show the chrysocolla surfaces are featureless.EDX analyses enable the formulae of the chrysocolla samples to be calculated.The thermal decomposition of the mineral chrysocolla has been studied using a combination of thermogravimetric analysis and derivative thermogravimetric analysis. XPS shows that there are two different copper species present, one which is bonded to oxygen and one to a hydroxyl unit. The O 1s is broad and very symmetrical suggesting two O species of equal number. The bond energy of 102.9eV for the Si 2p suggests that it is in the form of a silicate. The bond energy is much higher for silicas around ~103.5eV. The reported  Author to whom correspondence should be addressed (r.frost@qut.edu.au) P +61 7 3138 2407 F: +61 7 3138 1804 2 value for silica gel has Si 2p at 103.4eV. The combination of TG, PXRD, EDX and XPS adds to our fundamental knowledge of the structure of chrysocolla.

Support of dinuclear copper triketonate complexes on silica: Monolayer loading from complex footprint and the first crystallographically characterized cis dipyridine adduct

“…The calculated weight loss for the first reaction is 52.1% in agreement with the TGA results. The second reaction, which is known to occur readily at modest temperatures [31], yields a predicted weight loss of 8.8% which agrees with the observed weight loss of 9%. The TGA data suggest that most of the daa ligands are volatized at temperatures below 280 o C. The thermal decomposition results for the silica supported Cu 2 (daa) 2 samples are reported in Table 2.…”

Glycerol dehydration to hydroxyacetone in gas phase over copper supported on magnesium oxide (hydroxide) fluoride catalysts

“…Cu-MgFOH, two Cu species seem to be present, one with a Cu 2p3/2 binding energy of 932.8 eV and the other with a Cu 2p3/2 binding energy of 936.1 eV. These are consistent with Cu(II) species and the latter is consistent with Cu(OH) 2 as proposed by Frost et al[50].Nevertheless the presence of CuF 2 cannot be excluded since fluoride atom are present in the support and can react with copper species. The formation of such species would confirm the reaction between copper and the support during the calcination step.For the Cu-MgF 2 sample a single and intense peak centered at 932.1 eV is visible, while no satellite peaks are observed indicating that there is no Cu 2+ but the presence of reduced copper species.…”

The structure of hydrated copper-silicate gels, an analogue compound for natural chrysocolla

“…The first two weight loss steps in the TG curves for our synthetic gel samples are consistent with the loss of water and dehydration of hydroxyls of natural chrysocolla samples (Frost et al, 2012). DTA curves of Cu1Si1 and natural chrysocolla show exothermic peaks at around 680 °C, which correspond to the thermal decomposition reaction to form crystalline CuO (tenorite).…”

“…Although exothermic peaks are not clearly shown in cases of Cu1Si2 and Cu2Si1, similar reaction associated with the formation of CuO could be confirmed by heating them at 1000 °C. Frost et al (2012) pointed out that weight loss steps of natural chrysocollas are completely different from those of Cu(OH) 2 (spertiniite) which is well known to show the thermal decomposition reaction at about 160 °C. Thus, each of the synthetic gel samples is not a simple assem- blage of spertiniite and amorphous or crystalline silica but it includes the substance similar to chrysocolla.…”